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Aim
A well docked stable patient interface (PI) with minimal patient discomfort. The new SoftFit PI makes this step intuitive and simple.
Principles
Measure the patient’s pupil dilation before wheeling them to the femtosecond laser as it interrupts patient flow if you have to wheel them out again while they continue to dilate.
Use a guarded Leibermann-style speculum with a drop of Benoxinate for anaesthesia. Sedation is not required and IV sedation should be avoided as the patient should be compliant. The cornea should be moist when the PI is positioned but probably not over wet.
Make sure the patient’s eye is parallel to the laser, and centered in the speculum gap. Raising the patient’s chin may assist. This will decrease “lens tilt” as the laser will be perpendicular to the cornea.
It is useful to note if the patient has significant arcus before the docking takes place. Once the eye is docked, the arcus resembles the sclera and a definite boundary is not always easy to see. You might be tempted to move the incisions too centrally as you mistake the arcus for the sclera. This is easy to avoid with experience and checking for the arcus soon becomes second nature.
Some patients have excessive fatty cheek pads and floppy lids. Putting in the speculum then pushes the eyelids onto these cheek pads and limits the amount of opening of these lids. As the eyelids are floppy, opening the speculum wider can cause the lids to roll in. Have a look and confirm that the speculum is sitting snugly.
If the nose is prominent, turn the head turned slightly towards the machine for right eye or slightly away from the machine for left eye to keep nose from touching the PI. Excessive rotation should be avoided as this may have the PI contact the lateral canthus.
The SoftFit insert is placed in the PI after the application of a lubricant. The PI is then inserted onto the laser and the fit of the SoftFit Insert checked on the monitor. Bubbles can be manually expressed.
The PI is best positioned just at the eyebrow to allow for sufficient movement of the joystick control.
Lubricate the cornea and move the PI until it moves anterior to the cornea and watch from the side while you slowly lower the PI. You will see if the lid or speculum is in the way.
If the PI touches the patient’s nose or the speculum, the pressure on the sensor will increase without you seeing a “wave “of fluid on the cornea. Reposition the PI and dock again.
Don’t hover once you’re central and clear of the lids (you are not a helicopter pilot). Descend and dock.
A “wave “of fluid is seen to cross across the cornea. Once it crosses the center point, suction is applied and the joystick turned so that the pressure bar is in the green.
If corneal folds are seen on the screen, the power needs to be increased on the computer to ensure a free cut through the anterior capsule. This happens in less than 1 in 50 cases.
The PI is forgiving in terms of the ability to maneuver centration and incisions but is best placed to expose the lateral limbus and with the globe well centered. If the eye is excessively rotated superiorly the corneal incisions may be oblique and the nucleus will be tilted. For final adjustments just tapping the joystick allows for finer control.
With suction engaged commence the positioning of the various elements (limbus, centration of capsulorhexis, size of capsulorhexis, depth of nuclear cuts and the corneal incisions). The rhexis size can be reduced to avoid contact with a small pupil down to 4.4 mm. A 0.5 mm clearance is sufficient.
In vary few cases the contact lens comes off the SoftFit and remains on the cornea after the procedure. This can be gently removed. I do not try look for the contact lens on the eye straight after the procedure as the PI is in the way. Rather I look at the screen and see if I can see the SoftFit contour and the small white line showing where the incision was made. Only if I cannot see the outline on the screen do I look at the patient’s cornea.
Tip
Wait for the audible click before applying the laser treatment. If you eagerly press the foot pedal before the click, an error message will appear. Simply reset the treatment and then press the foot pedal again.
During the treatment note the suction pressure. If it falls or the limbal contact is lost then the corneal incisions which are undertaken last may be aborted. If treatment has commenced and suction is lost do not reengage but go to a manual procedure as it is impossible to accurately line up a partial treatment.
Do not be afraid if you have placed a gentian violet dot on the cornea to mark the axis of a toric lens as the femtosecond laser is not impeded by this.